Electrolytic cell for removal of material from a solution

ABSTRACT

An electrolytic cell for the recovery of material as a powder or flakes from a solution, includes a cell cavity for containing the solution, a rotatable electrode in the cavity having a pair of opposite electrode faces, and a counter electrode in spaced and opposing relationship with the respective opposite electrode faces of the rotatable electrode to supply a current through solution in the cavity to permit extraction of the material by electrochemical reaction. A vibrator directs vibrational energy toward the rotatable electrode to dislodge material extracted as a powder or flakes from the solution by an electrochemical reaction.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 10/941,900, filed Sep. 16, 2004, the contents of which are hereinincorporated by reference.

FIELD OF THE INVENTION

The present invention relates to an electrochemical method and apparatusfor recovering materials from solution by electrowinning orelectrooxidization.

BACKGROUND OF THE INVENTION

The concept on recovering materials from solutions by electrolysis isnot new. Many industries, such as plating processes, mining processesand metal finishing, produce waste product of solutions containing ionsof metals, and recovery of these metals are both environmentally andeconomically beneficial. Waste from solutions with unrecovered metalincreases the amount of sludge disposed on land-fields. Many systems ofmetal recovery currently use a mechanical device such as a blade, toremove deposited material from an electrode. The use of a mechanicaldevice has the disadvantages of increased wear, risk of breakage, andtendency to slow the treating process down.

Our copending U.S. application Ser. No. 10/941,900 describes an improvedmethod for recovering materials. This solution, which employs anelectrode rotating at high speed, has proved to be remarkably effective.

SUMMARY OF THE INVENTION

The present invention builds on the success of the invention disclosedin our copending application by improving the throughput. The inventionis capabable of either processing a higher volume of material in thesame sized cell or alternatively reducing the size of the cell for agiven throughput.

According to the present invention there is provided an electrolyticcell for the recovery of material as a powder or flakes from a solution,comprising a cell cavity for containing the solution; a rotatableelectrode in the cavity having a pair of opposite electrode faces;counter electrode portions in spaced and opposing relationship with saidrespective opposite electrode faces of the rotatable electrode to supplya current through solution in the cavity to permit extraction of thematerial by electrochemical reaction; and a vibrator for directingvibrational energy toward the rotatable electrode to dislodge materialextracted as a powder or flakes from the solution by an electrochemicalreaction.

In one embodiment the rotatable electrode is a cathode, which is in theform of a double-faced cylinder having internal and external faces. Thesecond electrode portions form part of a common anode and are defined bythe inwardly facing surfaces of an annular channel receiving thecylindrical cathode. Alternatively, the second electrode portions couldbe separate elements facing the opposite faces of the cathode. Therotatable electrode should preferably have a tangential speed in excessof 1 m/s, in which case it is desirable to provide a meniscus breaker toinhibit the rising tendency of liquid in the cell.

The structure of the electrodes can take various forms. In oneembodiment, the rotatable electrode is a cylinder, as noted above, but,for example, the rotatable electrode, cathode in the case ofelectrowinning, could also have a grating or mesh structure, or could beporous so as to have a three dimensional sponge structure.

The apparatus can be used for the recovery of metal from either anaqueous or non-aqueous solution, enabling facile separation ofelectrochemically deposited metal or metallic compounds from anunderlying cathode.

In one embodiment the formation of a powder, or flakes, removed byultrasonic or other mechanical vibrational energy, occurs on adouble-face rotatable electrode. This type of electrode may comprise ahollow disk or cylinder open at both ends to allow the solution to betreated to travel inside and outside the electrode. Hence, a powdery orflaky deposit obtained by electrochemical means can be formed on bothsurfaces of the double-face rotatable electrode and removed with anultrasonic or other type of vibrating device either on one or bothsurfaces of the electrode.

In one embodiment, an internal double-face counter-electrode is placedaround the double-face rotatable electrode to permit current flow. Eachsurface of the double-face rotatable electrode, both inner and outersections, faces a surface of the double-face counter-electrode. Thedouble-face rotatable electrode is placed in a sandwich-like fashioninside the cell cavity. More than one double-face electrode can be builtto fit inside a cell cavity.

The invention provides a type of double-faced rotatable electrode that,for the same throughput, is reduced in size compared with the rotatableelectrode disclosed in U.S. application Ser. No. 10/941,900. The size ofthe present double-face rotatable electrode is reduced at least by halfwhen both sides of its cylindrical surfaces are being used to extractmetals or oxidize organics from a solution to be treated.

The double-face counter-electrode can be placed in such a way that bothelectrode surfaces (anode and cathode) face one another in a parallelfashion. Preferably, the distance between both inner and outer faces isequal in order to achieve symmetry in the assembly, thus providingsimilar electrochemical conditions for both surfaces of the double-facerotatable electrode. Alternatively, the distance between each pair ofelectrode and counter-electrode can be adjusted in such a way that adifferent tangential speed is obtained. Hence, electrochemicalproperties that link this latter parameter to the reactor efficiency arerespected.

In one embodiment, the double-face rotatable electrode forms a cathode,and the double-face counter-electrode forms an anode, wherein metal inthe solution is deposited on the cathode as a metal powder or flakes,such that the ultrasonic energy displaces the metal powder from thecathode. In another embodiment, the double-face rotatable electrodeforms an anode, and the double-face counter-electrode forms a cathode.This embodiment is suitable for extracting organic waste, which isdeposited on the anode.

Since ultrasonic or other vibrating energy is present inside the cellcavity to remove the powdery, or flaky, deposit off the double-facerotatable electrode, a device propagating or generating the energyshould be placed toward the outer and/or the inner surfaces of thedouble-face rotatable electrode. Such device can be placed along thesame plane of the counter-electrode location. When non-retractableultrasonic generators are selected as a powder, or flakes, removaldevice for a specific electrochemical reaction, at least one generatormay be placed on both faces of the double-face rotatable electrode.

Depending upon the size of the cell cavity and the number of double-facerotatable electrodes used, the number and dimensions of the generatorscan be limited. For a determined electrolytic cell size, the limitationconcerns the number of generators that can be placed within the internalholder. The number of ultrasonic generators that can be fitted insidethe holder is limited by the size and the number of the transducersplaced inside the generators, an thus by the size of the generatorhousing itself.

In one embodiment the solution to treat is passed along both rotatingfaces of a double-face rotatable electrode, preferably at the same flowrate on each side. Furthermore, when more than one double-face rotatabledisk or cylinder turn together, since they are fixed to the samerotating shaft, each disk or cylinder turns at a different tangentialspeed for a fixed rotating speed (rpm) since the diameter of each diskor cylinder is different. This property can be especially useful whentwo or more metals are to be electrowon within the same solution to betreated.

Ultrasonic generators or any other mechanical vibrating device which canbe used for the removal of powder, or flakes, can be placed inside thereactor in either a static or dynamic (retractable) manner, facing onlythe outer or inner face or both faces of the double-face rotatableelectrode. When a static arrangement is employed, the double-facerotatable electrode requires at least one device for each face. When adynamic arrangement is employed, at least one single device can belocated toward the inner face only or the outer face only. A slidingmechanism can be used to withdraw it from one face and introduce infront of the other. The thickness of the double-face rotatable electrodecan be thin enough to transmit the energetic effect of the vibratingdevice.

The dynamic arrangement involves a contact between the vibrating deviceand the rotatable electrode. The device can be located inside a housingand, when needed, a mechanism slides the device toward the electrode andtouches it in order to transmit its energy for the time period it takesto remove all the powdery, or flaky, deposit from the two faces of thedouble-face rotatable electrode.

The sliding mechanism involves any type of actuator, piston, spring,blade, cushion or other similar element that allows a mechanicalmovement in one or two axes, vertically or horizontally. Hence, themovement provides a retractable motion of the vibrating device that isbeing used only when needed. Thus, the device does not impede therotating motion of the rotatable electrode. More than one such devicecan be placed inside the electrochemical reactor, targeting the removalof the powder, or flakes, from both rotatable electrode surfaces.

The electrolytic cell may further comprise a bin for collecting thematerial removed from the rotatable electrode, such as powdered or flakymetal from the cathode, or organic waste from the anode.

The electrolytic cell may be equipped with a device that has theproperty of breaking the liquid rise effect caused by the rotationmovement of the rotatable electrode. Such device, referred to as a“meniscus-breaker”, is required when the tangential speed (U) of theelectrode is higher than 1 m/sec, which is desirable in order to provideextraction removal of the powder. The order of magnitude of the rising(R) of the liquid level above its nominal value (liquid level when U=0)is given by the following relationship:R=U ²/4g; where g is the acceleration due to gravity.

The geometry and dimensions of the meniscus-breaker are determined fromthe following consideration: a) evolution of hydrogen, oxygen and otherpossible gases produced at the electrodes during the electrolysisprocess, b) liquid section above the meniscus-breaker that has to godown through the center hole of the device for being treated, c)presence of solid particles within that liquid (e.g. metallic powder).Because of these considerations, the bottom section of themeniscus-breaker should have a conical or pyramidal shape while theupper section should have an inverted similar shape on top of the bottomsection, given an overall hour-glass shape. The angle present withinboth sections must be such that the bottom section allows the gases toexit upwardly toward the center hole of the meniscus-breaker (where theshaft of the double-face rotatable electrode goes through) while theupper section allows the liquid charged with the solid particles (mostlymetallic) to go back into the cell by gravity. To be efficient, themeniscus-breaker should be located below the nominal level of the liquidinto the cell. Its rim (or borders) must closely touch the inner wall ofthe cell in such a manner that no liquid can go between the wall and themeniscus-breaker.

The present invention makes it possible to substantially reduce, atleast by half, the size of the rotatable electrode used and, thus, thesize of the electrolytic cell, when both sides of the rotatableelectrode are being used. Furthermore, it is also possible to extend theuse of both faces of more than one double-face rotatable electrode.Indeed, several disks, or cylinders, can be inserted inside one another,creating an array of electrodes of alternate polarity, turning atdifferent tangential speed and simultaneously working at various currentdensities.

Since both faces of the double-face rotatable electrode are being usedto produce a deposit, an inner surface and an outer surface call out fortwo or more ultrasonic generators to remove such deposit.

Embodiments of the invention permit the selective purification ofconcentrated electrolytes from undesired low concentration metalliccontaminants present into them. Furthermore, the invention can also beused to destroy organic contaminants present in low concentration ininorganic or organic conductive electrolytes by electrooxidation. Thedesired electrochemical reaction is achieved depending upon the inducedpolarity of the double-face rotatable electrode.

In another aspect the invention provides a method for extractingmaterial from a solution comprising providing an electrolytic cellincluding a rotating electrode having a pair of opposite electrode facesand counter electrode portions in spaced and opposing relationship withsaid respective opposite electrode faces of the rotating electrode;introducing a solution containing the material into the electrolyticcell; applying a direct current to the solution between the electrodesso that the material becomes deposited on both said opposite faces ofthe rotating electrode as a powder or flakes by electrochemicalreaction; and dislodging the material as a powder or flakes from therotating electrode with vibrational energy.

Other aspects and advantages of embodiments of the invention will bereadily apparent to those ordinarily skilled in the art upon a review ofthe following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a high-level illustration of an electrolytic cell inaccordance with the teachings of this invention;

FIG. 2 is a schematic cross-section of the cell cavity of theelectrolytic cell containing one double-face rotatable electrode;

FIG. 3 shows an example of an internal retractable ultrasonic generatorlocated inside the internal holder and facing the inner surface of therotatable electrode;

FIG. 4 illustrates the geometric relationship between the internalelectrode diameter and the available space location for the ultrasonicgenerator; and

FIG. 5 illustrates the electrolytic cell of FIG. 1 in an industrialapplication. This invention will now be described in detail with respectto certain specific representative embodiments thereof, the materials,apparatus and process steps being understood as examples that areintended to be illustrative only. In particular, the invention is notintended to be limited to the methods, materials, conditions, processparameters, apparatus and the like specifically recited herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus provided by the invention may be used either forelectrowinning metals or oxidizing organic compounds. The operation ofthe apparatus is selectively changed by changing the polarization of adouble-face rotatable electrode, as is described below.

Referring to FIG. 1, which in schematic form, is an overall view of anapparatus in accordance with the invention. It comprises an electrolyticcell 10 with a cell housing 12. The cell housing 12 defines a cellcavity 14 containing the electrodes. The shape of the housing 12 is notlimited. It may be composed of any suitable material so long as thehousing is electrically insulated from the double-face electrodes.Generally, the housing is cylindrical, although other shapes arepossible. In this embodiment, it is shown to be funnel-shaped. The cell10 contains a double-face rotatable electrode, where the powdery orflaky deposit is formed, as will be described in more detail withreference to FIG. 2.

A rectifier 16 provides the necessary current and voltage requiredbetween the electrodes to generate the electrochemical reaction in thecell for producing the powdery deposit when the double-face rotatableelectrode is polarized cathodically or to oxidize organic contaminantswhen the double-face rotatable electrode is polarized anodically.

The current is supplied to the electrodes by electrical busbars 26, 28.At least two electrodes, namely a cathode and an anode, are connected tothe cathode and anode busbars 26, 28, respectively. The double-facerotatable electrode can be polarized as the cathode or as the anode. Thedouble-face rotatable electrode can also be called the workingelectrode, and the double-face static electrode is called thecounter-electrode.

The housing 12 includes an inlet port 18 and flow passage 20 for feedingthe feedstock solution to be treated from a storage tank (not shown) tothe cell 10, and an outlet port 22 for removal of the solution, bothbeing effected by a pump 24. When the powder or flakes is beingdeposited as a result of the electrochemical reaction the solution willbe depleted of metal or organic contaminant. The depleted solution ispassed through a tank 32 containing a filter 52 (this number refers toFIG. 5) to a wastewater facility, or is being recycled in theoriginating process. In the case of a solution containing copper, it isfound that even during the deposition stage some powder becomesdislodged and is entrained with the depleted solution to the filter 52.

Periodically, during use the current is switched off and ultrasonicenergy is applied to the double-face electrode to dislodge the powder orflakes formed thereon. The current may be stopped periodically dependingupon the electrowinning cycle for anywhere from a few seconds to severalminutes. For instance, the current can be interrupted to activate theultrasonic generator for 10 seconds every 20 minutes of electrowinningcycle in a process to recover copper. Typically during the dislodgementphase the speed of rotation of the double-face rotatable electrode isreduced at 25% its nominal rotating speed.

When the powder or flakes is being dislodged from the double-faceelectrode by the application of ultrasonic energy, the dislodged powderis entrained in the liquid flowing through the outlet and subsequentlypassed through the filter 52 for removal. Since the liquid flowingthrough the cell in this phase is not depleted, the resulting liquid,after flowing through the tank 32, is switched to a buffer tank (notshown) rather than the wastewater facility. The liquid in the buffertank can be subsequently returned to the cell for further processingduring a subsequent deposition stage.

The cell 10, according to principles of the invention, also includes anultrasound generator having an oscillator 30 and ultrasound transducers50 (in FIG. 3) for directing ultrasonic energy at the double-facerotatable electrode during the powder removal phase. Other forms ofvibrational energy can also be applied to dislodge the powder or flakes.

The construction of the electrodes will be seen in more detail in FIG.2, which is an apparatus for the recovery of metals. The double-facerotatable electrode 5 is a distinct discrete component separate from thehousing mounted on a drive shaft 1. This type of electrode comprises ahollow disk or cylinder opened from both ends to allow the solution tobe treated to travel inside and outside the electrode. In FIG. 2, thedouble-face rotatable electrode 5 is shown as a hollow cylinder. Thiselectrode has opposite faces 5 a, 5 b on the inner and outer wallsrespectively. The double-face rotatable electrode 5 is being made of asuitable conductive material including stainless steel, titanium and itsalloy aluminum, or any other conductive material such as graphite.

The counter-electrode 11 is also situated within the cell 10. Thematerial of the counter-electrode 11 is not limited in any particularway and may be selected from any material typically used in the art.Usable materials may include stainless steel, platinized titanium, lead,DSA-type coating or graphite, among others. In this embodiment, thecounter-electrode 11 defines an outer annular channel 11 c having innerand outer walls providing electrode portions 11 a, 11 b respectivelyopposing the electrode faces 5 a, 5 b of the cathode 5, although it willbe appreciated that the electrode portions 5 a, 5 b could be separate.The annular channel 11 c, which in this embodiment provides adouble-faced cathode, thus serves to receive the cylindrical anode in asandwich-like manner.

Thus, it will be seen that the internal double-face anode is placedaround the double-face rotatable cathode to permit current flow throughthe solution. Each surface of the double-face rotatable cathode, bothinner and outer sections, faces a surface of the double-facecounter-anode. Preferably, the distance between both inner and outerfaces is equal in order to achieve symmetry in the assembly, thusproviding similar electrochemical conditions for both surfaces of thedouble-face rotatable electrode. Alternatively, the distance betweeneach pair of electrode and counter-electrode can be adjusted in such away that a different tangential speed is obtained.

The electrolytic cell 10 has an internal support 9 mounted on legs 42,which hold the internal section of the double-face counter-electrode 11connected to its external sections 6 and 40. The support 9 can holdseveral double-face counter-electrodes, up to a number equal to thenumber of double-face rotatable electrodes. The support 9 also holds thevibrating device(s) 50 such as an ultrasonic generator as shown on FIG.3, that can be retractable or not, as is described below. The legs arefixed such that the liquid is free to flow toward the cell outlet 22.

The electrolytic cell has a rim 2 that prevents liquid overflow. Thisrim, or border, can also be used to hold a ventilation dock, and anintlet tubing 20 (from FIG. 5) connected to the tank where the liquid tobe treated comes from. A second rim below the previous one supports themeniscus-breaker 27 where the rotating shaft 1 of the double-facerotatable electrode 5 goes through.

The double-face rotatable electrode may be equipped with a cap 4 overand under the top section of the double-face rotatable electrode and aring 7 at the bottom edge in order to mask areas on the electrode wherethe electrochemical reaction is not desired and/or to control theelectrical field lines present within the electrolyte when a current isbeing applied between the double-face electrodes, in such a manner thatthe deposit becomes as much uniform as possible over the double-facerotatable electrode.

The double-face counter-electrode is placed in such a way that bothelectrode surfaces (anode and cathode) are facing one another in aparallel fashion. Preferably, the distance between both inner and outerfaces is equal in order to achieve symmetry in the assembly, thusproviding similar electrochemical conditions for both surfaces of thedouble-face rotatable electrode. Alternatively, the distance betweeneach pair of electrode and counter-electrode can be adjusted in such away that a different tangential speed is obtained. Hence,electrochemical properties that link this latter parameter to thereactor efficiency are respected.

The shape of each of the double-face electrodes 5 and 11 should allcorrespond with one another. For example, if the anode is cylindrical,the cathode will be a cylindrical and coaxial with the anode. In thedescribed embodiment, suitable for recovering metals, the electrode 5 isthe cathode and the electrode 11 is the anode. The roles can bereversed, for example, for the oxidation of organic material, in whichcase the electrode 11 would become the cathode and the electrode 5 theanode. In this latter case, the material shall be so selected that itwill not dissolve, passivate, anodize or be destroyed by any chemical orelectrochemical effect.

There is a relationship between the current density and the liquid flowrate that an electrolytic cell has to treat. The solution to be treatedtravels along both faces of the, for example, cylindrical section of thedouble-face rotatable electrode. The liquid flows between the inner andthe outer surfaces of the double-face rotatable electrode and thedouble-face counter-electrode, preferably at the same flow rate. To goinside the double-face rotatable electrode, the liquid goes throughopening or apertures on top of it. The opening can be as wide aspossible, as long as there are some structural elements that hold therotating cylindrical section to the central shaft. The opening can bemade of several holes, curved or straight slots, of various lengths,diameters and/or geometries, all depending upon the number ofdouble-face rotatable electrodes that are fixed altogether.

Depending upon the size of the cell cavity and the number of double-facerotatable electrodes used, the number and dimensions of the generatorscan be limited. For a particular electrolytic cell size, the limitationconcerns the number of generators that can be placed within the internalholder. The number of ultrasonic generators that can be placed insidethe holder is limited by the size and the number of the transducersplaced inside the generators, thus, by the size of the generator housingitself.

FIG. 4 illustrates the geometric relationship between the rotatableelectrode inner surface REIS and the ultrasonic generator size. With asimplified geometry of generators built with a width that is symmetricalto its depth, it is possible to calculate the number and/or the limitingdimension of the generators that can be placed inside the internalholder (that faces the inner surface of the double-face rotatableelectrode), using the following equations:L ² +L ²=4r _(A) ²2L ²=4r _(A) ²2^(1/2) L=2r _(A)Since r _(A) =r _(C) −Y, thenL=2(r _(C) −Y)/2^(1/2)

The “X” value on FIG. 4 represents the distance between the face of thegenerator that generates the ultrasounds and the internalcounter-electrode radius. The “Y” value corresponds to the distancebetween the counter-electrode and the rotatable electrode inner surface(REIS). The “L” value is the actual width of the generator and “r_(A)”is the radius of the counter-electrode.

In order to determine the value X and consequently, the distance “D”between the generator and the REIS, the following equations are beingused:(r _(A) −X)² =r _(A) ²−(L/2)²r _(A) −X=(r _(A) ²−(L/2)²)^(1/2)X=r _(A)−(r _(A) ²−(L/2)²)^(1/2)D=Y+(r _(A)−(r _(A) ²−(L/2)²)^(1/2))

This latter value is important since the ultrasonic energy may becomeweaker as the distance between the generator and the REIS increases. Theequation stands for a non-retractable generator. For a retractablegenerator, the equation shall take under consideration the length of thepath that the generator travels before it touches the rotatableelectrode. The minimum size of the holder diameter will be increasedaccording to the width of the generator plus the length of the path.Therefore, the dimension of the REIS limits the overall size and numberof generators.

Regardless of the target application or operation of the apparatus, theworking electrode is the one that rotates. The rotatable electrode isthe electrode where the target reaction occurs. The rotatable electrodecan therefore be polarized cathodically or anodically.

The source 16 of direct electrical current that is mounted on theelectrolytic cell frame 69 is connected between the anode and cathodevia leads 26, 28 to allow current to flow. When the double-facerotatable electrode is polarized cathodically, metal ions in solution inthe cavity migrate toward the cathode where the metal is deposited.Therefore, the cathode rotates to improve the mass transport and reducethe thickness of the diffusion layer. The cathode is rotated by meanssuch as one rotating shaft which may be made of the same metal as thecathode, through which the electric current is fed and which rotate intwo bearings formed in walls of the cell. Rotation of the cathode can beachieved by means of an electric motor (not shown on FIG. 1) through aspeed controller (not shown). Although the double-face rotatableelectrode 5 is shown to rotate counter-clockwise, the direction ofrotation may also be clockwise.

When more than one double-face rotatable electrode 5 is used to treat acertain volume of solution, they can be connected in parallel or inseries in order to achieve the desired electrochemical reaction ortargeted chemical concentration level. Each double-face rotatableelectrode 5 can operate under similar or different operation modes.

When the current flows between the anodically polarized electrode andthe cathodically polarized electrode, the current is ideally distributedevenly on both sides of the facing electrodes. For instance, when thedouble-face rotatable electrode is made a cathode, the current densityon both inside and outside surfaces is identical, as well as the anodiccurrent density flowing within all anodes. When more than onedouble-face rotatable electrode are present, it is possible toelectrically isolate one double-face rotatable electrode from oneanother and connect them to a separate power supply, in such a way thatthe desired current density, coupled to a desired rotating speed isobtained to electrowin a metal specifically or to oxidize an organicspecies specifically.

Furthermore, when more than one double-face rotatable disk or cylinderturn together, since they are fixed to the same rotating shaft, eachdisk or cylinder turns at a different tangential speed for a fixedrotating speed (rpm) since the diameter of each disk or cylinder isdifferent. This property can be especially useful when two or moremetals are to be electrowon within the same solution to be treated.

FIG. 3 shows where a device 50 such as an ultrasonic generator may belocated. Such device can be retractable (dynamic) or static, beinglocated inside the holder and/or within the double-face rotatableelectrode.

When a static fashion is selected, the double-face rotatable electroderequires at least one device for each face.

When a dynamic arrangement is selected, at least one single device canbe located toward the inner face only or the outer face only; thethickness of the double-face rotatable electrode can be thin enough totransmit the energetic effect of the vibrating device. The dynamicfashion involves a contact between the vibrating device and therotatable electrode.

The device can be located inside a housing and when needed, a mechanismslides the device toward the electrode and touches it in order totransmit its energy upon it for the time period it takes to remove allthe powdery, or flaky, deposit from the two faces of the double-facerotatable electrode.

The sliding mechanism can be any type of actuator, piston, spring,blade, cushion or other similar element that allows a mechanicalmovement in one or two axes, vertically or horizontally. Hence, themovement provides a retractable motion of the vibrating device that isbeing used only when needed, thus, the device does not impede therotating motion of the rotatable electrode. More than one such devicecan be placed inside the electrochemical reactor, targeting the removalof the powder, or flakes, from both rotatable electrode surfaces.

There may be as many devices as the available space volume allows. Thedevices are preferably connected to one another, or alternatively theymay be separate. During an electrowinning process, it is preferable toactivate the device to remove the powder, or flakes, at the end of theextraction cycle, hence, synchronizing all energetic devices at once.The vibrating device can be located horizontally or vertically withrespect to the double-face rotatable electrode. When placed vertically,in a retractable fashion especially, the generator shall touch therotatable electrode between the ring 7 and the cap 4 for a directmetal-to-metal contact.

It should be understood that the term “ultrasonic” embraces soundvibrations capable of causing a cavitation effect sufficient to dislodgethe powder or flakes from the electrode whether strictly beyond theaudible range or not. A suitable range is 16 to 40 KHz, with 25 KHzbeing preferred.

The present invention employs the ultrasonic generator for the removalof deposit from the inner surface of the rotatable electrode, and inaddition such a generator can be retractable, hence, physically touchingthe rotatable electrode when idle. Other type of vibrating devices canalso be considered. When physical available spaces between electrodesprevent the insertion of ultrasonic generators, other coating removalmethods shall be considered.

The opening of the cap 4 matches the aperture of the double-facerotatable electrode 5. Hence, there is no obstacle for the liquid toflow between the inner face of the double-face rotatable electrode andthe internal section of the double-face counter-electrode 11. The formof the opening can be of various geometries such as circles, triangles,etc. The opening is such that depending upon its size, the mechanicalconstraints of fabrication are at minimum and that service securityfactors are met.

The bridge between the internal and external double-facecounter-electrode sections may be masked and/or perforated; this isespecially true if expanded mesh is used as a substrate for a coatedmaterial like DSA-type anodes.

One or more bridges can be fixed, as long as the form and, shape ordimensions of the bridges do not interfere with the liquid flow ratewithin the cell and/or entraps powder or flaky particles. An unlimitednumber of bridges can be fixed, depending upon the number ofcounter-electrodes being used or from mechanical considerations(machining, welding, fixing parts). Minimum number of bridges is beingdetermined by the current intensity that travels across the section ofthe electrode bridge.

The internal holder may have a central hole that guides and secures theshaft position of the rotatable electrode when it turns at a tangentialspeed higher than 2.0 m/s.

The liquid flow rate across a double-face rotatable electrode may be atleast twice the value of a single-face one, because of its doubleelectrode surface area. On the other hand, if the liquid flow rate of asingle-face rotatable electrode has to be maintained and a double-facerotatable electrode has to replace the single-face rotatable electrode,the size of the double-face rotatable electrode has to be reduced atleast by half to keep the same electrode surface area. Hence, the sizeof the electrolytic cell is at least half the size of the original one.

FIG. 5 illustrates the electrolytic cell of FIG. 1 in an industrialapplication. Solution from storage tank 51 is pumped into the cell 10for processing by means of pump 54. The cell is fitted with anultrasonic level detector that controls the operation of pumps 24, 54 tomaintain the liquid in the cell at the desired level.

The liquid flowing out of the base of the cell 10 flows into the filterhousing 32 with the filter 52 for removing powder or flakes entrained inthe liquid exiting the cell 10 from the filter housing outlet 71.

The filter 52 can include filter bags arranged such that the liquidflows through their walls and deposits the powder or flakes within thebags for subsequent removal. Any suitable filter technology can beemployed for this purpose.

The busbar 26 is electrically connected to the double-face rotatableelectrode 5 by means of a brush connector 62 in contact with the shaft1. The shaft 1 is driven in rotation by a motor 64 and pulley system 66.The shaft rotates in bearings 68.

The electrolytic cell may preferably be equipped with a device 27referred to as a “meniscus breaker” that eliminates the meniscus risingeffect that becomes increasingly important when the tangential speedreaches about 1 m/sec and beyond. The device 27 has a “Chinese hat”shape, that is it is in the form of a disk with a central aperture 27 a,the disk having upper and lower surfaces 27 b tapering inwardly towardthe central aperture 27 a. This device prevents the meniscus from risingup the cell while permitting gases formed within the cell to escape.

In operation, a cathode and anode are put into the cell 10. The inletport is connected to the storage tank holding solution to treat, and thesolution is pumped via a pump from the tank into the cell cavity to fillthe cavity and close the circuit between the cathode and anode. The vastmajority of expected applications are in aqueous media, but in certaincases it could be in non-aqueous solutions or electrolytes (e.g.ethanol, benzoic acid, etc.). Preferably, enough solution is pumped intothe cavity to completely submerge both the cathode and the anode. Thesolution is suitably pumped into the cell cavity. For electrolysis, thetotal metal concentration of the solution is from 30 to 3000 ppm (mg/L),preferably between 50 to 1000 ppm (mg/L).

The cell can be supplied with any form of electric current, such asdirect current, alternating current, pulsed, periodic reverse pulse,etc. The anode and cathode of the electrolytic cell are connected to arectifier which controls the application of electrical power to theanode and cathode.

The apparatus of this invention can be used to produce metal powders orflakes when the rotatable electrode is cathodically polarized. Powdersor flakes may include metals or alloys in pure forms or metallichydroxides or oxides. The definition of a powder or a flake shall bebroad (grain size, shape, metal ceramic, metal, alloys etc.). Theformation of a powder or a flake, instead of a compact film of metal oralloy, allows the use of ultrasounds to remove the metal from thecathode (as is described below). For maintenance purposes, gathermaterial samples or for any other reasons, the apparatus is equippedwith a rising structure 70 that elevates and lowers the entire rotatablemechanism.

Deposition of metal powder is accomplished by the rigid control ofprocess parameters. The parameters to be controlled include: voltage,current density (pushed toward the limiting current) at the cathode,plating time, cathode rotation speed, electrolytic conditions throughproper adjustments of pH, composition, temperature, conductivity,viscosity, concentration, and other parameters to ensure that the metalprecipitates on the cathode (being reduced) as a powder or flakes. Thevoltage and current are selected by fixing the current level across theelectrodes at an optimum level for the range of concentrations found ina particular application. The current level has been determined byexperimentation. For instance, to produce zinc powder from anelectrolyte that contains only 100 ppm of this metal, a disk of adiameter 0.5 meter (two times its width) will turn at 175 rpm with acurrent density of 60 mA/cm². If the metal concentration is different,electrowinning conditions will be different as well. If the sought metalis copper instead of zinc, present at the same concentration, speed ofrotation and applied current will also be different. Electrowinningconditions are determined on a case by case basis.

As noted the metal powder or flakes produced at the cathode may beremoved periodically by switching off the current and applyingultrasonic energy. The metal deposit removal period may vary from oneelectrolyte to another. Preferably, the deposit does not exceed 10% ofthe distance between anode and cathode. For example, the preferred gapbetween electrodes is 2 cm, thus, a 0.2 cm thick deposit will be removedby using the ultrasonic device. Powder or flakes removal conditions canvary from one case to another. For instance, powder can be removed asper determined numbers of coulombs or thickness, depending upon powderproperties and electrolyte composition or reactor efficiency.

The ultrasonic generator 30 supplies an alternating-current energy at anexcitation frequency in an ultrasonic range, for example, from 16 kHz to40 kHz, 25 kHz being preferred. The ultrasonic electrical energy isconverted into ultrasonic mechanical vibrations at a frequencycorresponding to the excitation frequency. The mechanical vibrationsproduced by the transducers 50 are applied directly toward the cathodeto cause cavitation at the surface of the cathode. This effect causesthe metal powder to be removed from the electrode surface. For example,to remove a zinc powder deposit from the rotatable electrode, 2 to 4minutes of intense ultrasounds at 25 kHz every 24 hours of deposition issufficient to loosen the powder or flakes from the rotatable electrodeRequired ultrasonic energy to dislodge powder or flakes from a knownelectrode surface area is determined experimentally from solution tosolution. For instance, with a copper powder produced at 160 mA/cm2 at atangential speed of 10.88 m/s, it has been found that 1 watt/cm2 for 10seconds is enough to remove the powder completely when the tangentialspeed during the removal has been reduced to 2.72 m/s. The loosenedpowder or flaky deposit is subsequently collected by the filter 52.

The metal becomes deposited as discrete particles at the cathode and iscollected at the bottom of the cell, which is preferably conical orshaped as a funnel having a practical solid angle from 20 to 75 degrees,45 degrees being preferred, or as a loosely adherent deposit which maybe lifted from the cell and washed off the cathode. The metal powder orflakes accumulated at the bottom of the cavity can be removedperiodically or continuously through the bottom outlet on removal of aplug or through a valve. A collecting bin is located at the bottom ofthe cell, and collects the powdered or flaky metal removed from thecathode. The powder or flakes can be collected either by recoveringmetals from industrial process waters (plating shops, smelters, mining,etc.) and by producing a specific powder from a defined electrolyte.Electrolyte composition can be such that metal powder or flakes can bemade of a pure metal or alloys.

The apparatus of this invention may also be used to oxidize organiccompounds when the double-face rotatable electrode is anodicallypolarized. The double-face rotatable electrode is capable of destroyingorganic contaminants from organic or inorganic electrolytes. If foulingof the double-face rotatable electrode occurs during such application,ultrasonic cleaning is performed using the ultrasonic generators. Forexample, phenol or creosols can be electrooxidized from 1500 ppb (μg/L)down to 20 ppb (μg/L) using a rotatable electrode and cathode made ofstainless steel. The nature of the organic compounds to be destroyed,its concentration, and the material to use as electrodes such as anodeand cathode are not limited. The double-face rotatable electrode is mostefficient in destroying organic compounds found in low concentrations inorganic or aqueous solutions.

For return of the solution once treated either by electrowinning orelectrooxidation, the outlet port is connected to the original tank in aclosed loop fashion or to another tank for further use or disposal ofthe solution. When the double-face rotatable electrode works in a waythat the treated solution meets disposal rules and regulations (orconcentrations required by a specific process EX: 3000 ppm to 1000 ppmof zinc for the chromate bath), the treated solution may go directlyinto the sewer. Otherwise, the treated solution may be connected to aconventional wastewater system (or returned to the process). The flowrate of the liquid being treated is such that the volume of the liquidthat enters the inlet is the same than the one that comes out of theoutlet.

It can be seen that the cell can be employed repeatedly with the sameanode and cathode.

The method of the present invention may be illustrated in the followingexamples. These examples are provided for further illustrating thepresent invention, but are in no way to be taken as limiting.

EXAMPLE 1

If a single-face rotatable electrode is to be design to treat forinstance 40 liters/minute of a copper solution at 150 mA/cm², therequired surface of the cathode is 19635 cm² and its diameter is 100 cm;keeping the liquid flow rate but doubling the surface area reduces thecurrent by half; since the current density cannot be changed, thesurface area can only be kept at its original calculated value bydividing by half the diameter of the rotatable electrode. Hence, theoverall size of the electrolytic cell is being reduced by half when thesurface area of the rotatable electrode is doubled.

EXAMPLE 2

If two metals such as copper and nickel are to be electrowon atrespectively 150 mA/cm² and 50 mA/cm² and tangential speeds of 10.88 and5.44 m/s, two double-face rotatable electrode mechanically fixedtogether to the same shaft but electrically isolated from one each otherwill required a diameter difference of 2:1 and a total applied currentdifference of 3/2:1.

The invention is more adapted to recover metals from plating processesand mining processes, but can be applied to other types of industriessuch as metal finishing, metallurgy, pigments and chemical additives.The recovery of metals lowers the amount of generated waste when theapparatus is installed up-stream a wastewater system, thus, reducing theamount of sludge to dispose on land-fields.

Numerous modifications may be made without departing from the spirit andscope of the invention as defined in the appended claims.

1. An electrolytic cell for the recovery of material as a powder orflakes from a solution, comprising: a cell cavity for containing thesolution; a rotatable electrode in the cavity having a pair of oppositeelectrode faces; counter electrode portions in spaced and opposingrelationship with said respective opposite electrode faces of therotatable electrode to supply a current through solution in the cavityto permit extraction of the material by electrochemical reaction; and avibrator for directing vibrational energy toward the rotatable electrodeto dislodge material extracted as a powder or flakes from the solutionby an electrochemical reaction.
 2. The electrolytic cell of claim 1,wherein said counter electrode portions define a channel receiving saidrotatable electrode.
 3. The electrolytic cell of claim 2, wherein saidrotatable electrode is cylindrical and said counter electrode portionsdefine an annular channel accommodating a cylindrical wall of saidrotatable electrode, wherein inner and outer surfaces of saidcylindrical wall provide said opposite electrode faces.
 4. Theelectrolytic cell of claim 3, wherein said rotatable electrode and saidcounter electrode portions have a common axis.
 5. The electrolytic cellof claim 4, wherein the radial distance from an inner electrode portiondefining to the inner face of the rotatable electrode is the same as theradial distance from the outer face of the rotatable electrode to theouter electrode portion.
 6. The electrolytic cell of claim 1, furthercomprising a meniscus breaker to inhibit the rising of liquid in thecell at tangential speeds of the rotatable electrode in excess of 1m/sec.
 7. The electrolytic cell of claim 6, wherein the meniscus breakeris shaped to permit the passage of liquid and solid particles downwardlyand the evolution of gases from the cell upwardly.
 8. The electrolyticcell of claim 1, wherein said vibrator is an ultrasonic generator. 9.The electrolytic cell of claim 8, wherein the ultrasonic generator is infixed in said cavity and includes transducers facing said respectiveopposite faces.
 10. The electrolytic cell of claim 8, wherein theultrasonic generator is retractable so that it can direct ultrasonicenergy selectively to either of said opposite faces.
 11. Theelectrolytic cell of claim 10, further comprising a sliding mechanism toslide the ultrasonic generator into position relative to the rotatableelectrode.
 12. The electrolytic cell of claim 1, comprising a pluralityof said rotatable electrodes located inside the cell cavity.
 13. Theelectrolytic cell of claim 12, further comprising a plurality of sets ofsaid counter electrode portions located inside the cell cavity andassociated with said respective rotatable electrodes.
 14. Theelectrolytic cell of claim 3, further comprising an internal holder forguiding and securing a shaft of the rotatable electrode.
 15. Theelectrolytic cell of claim 14, wherein the internal holder is mounted onone or more legs placed in such a way that the holder is securely fixedinside the cell cavity and liquid flow is not restricted.
 16. Theelectrolytic cell of claim 13, where the electrodes are configured sothat the same current is applied to each one.
 17. The electrolytic cellof claim 1, wherein the ultrasonic generator is configured to workduring or after electrolytic deposition.
 18. The electrolytic cell ofclaim 3, wherein the cylindrical electrode has an opening to permitliquid to pass over either face of the rotatable electrode.
 19. Theelectrolytic cell of claim 1, wherein the rotatable electrode has asponge or mesh type grating configuration.
 20. A method for extractingmaterial from a solution comprising: providing an electrolytic cellincluding a rotating electrode having a pair of opposite electrode facesand counter electrode portions in spaced and opposing relationship withsaid respective opposite electrode faces of the rotating electrode;introducing a solution containing the material into the electrolyticcell; applying a direct current to the solution between the electrodesso that the material becomes deposited on both said opposite faces ofthe rotating electrode as a powder or flakes by electrochemicalreaction; and dislodging the material as a powder or flakes from therotating electrode with vibrational energy.
 21. The method of claim 20,wherein the direct current is switched off at intervals, and during saidintervals said vibrational energy is directed toward the rotatableelectrode.
 22. The method of claim 21, wherein said current is switchedoff for 1 to 4 minutes every 24-36 hours.
 23. The method of claim 20,wherein the tangential speed of the rotatable electrode is at least 1m/sec.
 24. The method of claim 20, wherein the solution contains a metaland the rotating electrode forms a cathode.
 25. The method of claim 20,wherein the solution contains an organic compound and the rotatingelectrode forms an anode.
 26. The method of claim 20, wherein therotating electrode and the counter electrode portions form a concentricarrangement.